How to deal with the nine problems of valves:

1、 Why can't the double seal valve be used as a shut-off valve

The advantage of the two seat valve core is the force balance structure, which allows a large differential pressure, while its prominent disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting off occasions, the effect is obviously not good. Even if many improvements have been made for it (such as double seal sleeve valve), it is not desirable.

2、 Why is the double seat valve easy to oscillate when working with a small opening

For single core, when the medium is flow open, the stability of the valve is good; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two valve cores, the lower valve core is in flow closed and the upper valve core is in flow open. In this way, when working with a small opening, the flow closed valve core is easy to cause the vibration of the valve, which is the reason why the double seat valve cannot be used for working with a small opening.

3、 What is the poor anti blocking performance of the straight stroke regulating valve and the good anti blocking performance of the angular stroke valve

The valve core of the straight stroke valve is vertically throttled, and the medium flows in and out horizontally. The flow channel in the valve cavity must turn upside down, which makes the flow path of the valve quite complex (such as the inverted "s" shape). In this way, there are many dead zones, which provide space for the sedimentation of the medium. In the long run, it will cause blockage. The throttling direction of the angle travel valve is the horizontal direction. The medium flows in and out horizontally, which is easy to take away the dirty medium. At the same time, the flow path is simple, and there is little space for medium sedimentation, so the angle travel valve has good anti blocking performance.

4、 Why did the sleeve valve replace the single and double seat valve, but it didn't work out

Sleeve valves, which came out in the 1960s, were widely used at home and abroad in the 1970s. Sleeve valves accounted for a large proportion of petrochemical devices introduced in the 1980s. At that time, many people believed that sleeve valves could replace single and double seat valves and become the second generation products. Up to now, this is not the case. Single seat valve, double seat valve and sleeve valve are all used equally. This is because the sleeve valve only improves the throttling form, stability and maintenance better than the single seat valve, but its weight, anti blocking and leakage indicators are the same as those of the single and double seat valve. How can it replace the single and double seat valve? Therefore, it can only be used together.

5、 Why is model selection more important than calculation

Compared with calculation and model selection, model selection is much more important and complex. Because calculation is only a simple formula calculation, it does not lie in the accuracy of the formula itself, but in the accuracy of the given process parameters. There are many contents involved in model selection. A little carelessness will lead to improper model selection, which will not only cause a waste of human, material and financial resources, but also the use effect is not ideal, resulting in a number of use problems, such as reliability, service life, operation quality, etc.

6、 Why is the service life of rubber lined butterfly valve and fluorine lined diaphragm valve used for desalted water medium short?

The desalted water medium contains low concentrations of acids or bases, which are highly corrosive to rubber. The corrosion of rubber is characterized by expansion, aging and low strength. The use effect of rubber lined butterfly valves and diaphragm valves is poor. The essence is that rubber is not corrosion resistant. The rear rubber lined diaphragm valve is improved to a fluorine lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine lined diaphragm valve cannot be folded up and down and is broken, causing mechanical damage and shortening the service life of the valve. Now the best way is to use special ball valve for water treatment, which can be used for 5 ~ 8 years.

7、 Why should the shut-off valve be hard sealed as far as possible

The lower the leakage of the shut-off valve, the better. The leakage of the soft seal valve is the lowest. Of course, the cutting effect is good, but it is not wear-resistant and has poor reliability. Judging from the double standards of small leakage and reliable sealing, the soft seal cut-off is not as good as the hard seal cut-off. For example, the full-function ultra light regulating valve is sealed and stacked with wear-resistant alloy protection, with high reliability and a leakage rate of 10 ~ 7, which can meet the requirements of the shut-off valve.

8、 Why is the stem of the straight stroke regulating valve thinner

It involves a simple mechanical principle: large sliding friction and small rolling friction. When the valve rod of the straight stroke valve moves up and down, and the packing is slightly compressed, it will wrap the valve rod tightly, resulting in a large return difference. For this reason, the valve stem is designed to be very small, and PTFE packing with small friction coefficient is often used for packing, so as to reduce the return difference, but the problem is that the valve stem is thin, it is easy to bend, and the service life of packing is also short. The best way to solve this problem is to use the travel valve stem, that is, the angle stroke regulating valve. Its stem is 2 ~ 3 times thicker than the straight stroke stem, and graphite packing with long service life is selected. The stem stiffness is good, the packing life is long, and its friction torque is small and the return difference is small.

9、 Why is the cut-off pressure difference of angle stroke valves larger?

The cut-off pressure difference of angle stroke valve is large because the resultant force of the medium on the valve core or valve plate produces a very small torque on the rotating shaft, so it can withstand a large pressure difference.